U.S. patent application number 10/529219 was filed with the patent office on 2006-03-16 for controller for construction machine and method for operating input torque.
This patent application is currently assigned to Hitachi construction machinery co., ltd.. Invention is credited to Hidetoshi Satake, Yukihiro Tatsuno.
Application Number | 20060056978 10/529219 |
Document ID | / |
Family ID | 32040309 |
Filed Date | 2006-03-16 |
United States Patent
Application |
20060056978 |
Kind Code |
A1 |
Tatsuno; Yukihiro ; et
al. |
March 16, 2006 |
Controller for construction machine and method for operating input
torque
Abstract
A control apparatus of a construction machine according to the
present invention includes a variable displacement hydraulic pump
(10) driven by a prime mover (20), a hydraulic actuator (5) driven
with pressure oil discharged from the hydraulic pump (10), and a
rotation speed detection means (31) for detecting an actual
rotation speed (Nr) of the prime mover (20). The control apparatus
includes a prime mover control means (40B) for controlling a
rotation speed of the prime mover (20) in accordance with an extent
to which the operating means (14a) is operated, and an input torque
control means (40A) for adjusting an input torque (T2) for the
hydraulic pump (10) based on a deviation (.DELTA.N) between the
actual rotation speed (Nr) detected by the rotation speed detection
means (31) and a control rotation speed (N.theta.) set through an
operation of the operating means (14a), and the input torque
control means (40A) executes control to decrease the input torque
(T2) if the control rotation speed (N.theta.) is greater than the
actual rotation speed (Nr) and the deviation (.DELTA.N) between
them is larger than or equal to a predetermined value (N2).
Inventors: |
Tatsuno; Yukihiro;
(Tsukuba-shi, JP) ; Satake; Hidetoshi;
(Ishioka-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Hitachi construction machinery co.,
ltd.
5-1, Koraku 2-chome, Bunkyo-ku
Tokyo
JP
112-0004
|
Family ID: |
32040309 |
Appl. No.: |
10/529219 |
Filed: |
September 26, 2002 |
PCT Filed: |
September 26, 2002 |
PCT NO: |
PCT/JP02/09967 |
371 Date: |
March 25, 2005 |
Current U.S.
Class: |
417/42 ;
417/1 |
Current CPC
Class: |
B60W 10/06 20130101;
E02F 9/2235 20130101; F04B 49/06 20130101; F04B 49/20 20130101;
F16H 61/472 20130101 |
Class at
Publication: |
417/042 ;
417/001 |
International
Class: |
F04B 49/00 20060101
F04B049/00 |
Claims
1-8. (canceled)
9. A control apparatus of a construction machine that includes: a
variable displacement hydraulic pump driven by a prime mover; a
hydraulic actuator driven with pressure oil discharged from the
hydraulic pump; and a rotation speed detection device that detects
an actual rotation speed of the prime mover, comprising: a prime
mover control device that controls a rotation speed of the prime
mover in accordance with an extent to which an operating member is
operated; and an input torque control device that adjusts an input
torque for the hydraulic pump based on a deviation between the
actual rotation speed detected by the rotation speed detection
device and a control rotation speed set through an operation of the
operating member, wherein: the input torque control device executes
control to decrease the input torque if the control rotation speed
is greater than the actual rotation speed and the deviation between
them is larger than or equal to a predetermined value.
10. A control apparatus of a construction machine that includes: a
variable displacement hydraulic pump driven by a prime mover; a
hydraulic actuator driven with pressure oil discharged from the
hydraulic pump; and a rotation speed detection device that detects
an actual rotation speed of the prime mover, comprising: a prime
mover control device that controls a rotation speed of the prime
mover in accordance with an extent to which an operating member is
operated; and an input torque control device that adjusts an input
torque for the hydraulic pump based on a deviation between the
actual rotation speed detected by the rotation speed detection
device and a control rotation speed set through an operation of the
operating member, wherein: if the control rotation speed is greater
than the actual rotation speed and the deviation between them is
larger than or equal to a predetermined value, the input torque
control device executes control to decrease the input torque by an
amount which is greater than an amount set when the deviation is
below the predetermined value.
11. A control apparatus of a construction machine according to
claim 9, wherein: the input torque control device sets an
adjustment amount of the input torque to zero if the control
rotation speed is greater than the actual rotation speed and the
deviation between them is below the predetermined value.
12. A control apparatus of a construction machine according to
claim 9, wherein: the input torque control device executes control
to increase the input torque in correspondence with increase in the
deviation if the control rotation speed is smaller than the actual
rotation speed, and if the control rotation speed is greater than
the actual rotation speed and the deviation between them is larger
than or equal to the predetermined value, a rate of change of the
input torque is set greater than a rate of change of the input
torque set when the control rotation speed is smaller than the
actual rotation speed.
13. A control apparatus of a construction machine according to
claim 9, wherein: the hydraulic actuator is a hydraulic motor for
traveling, and the operating member is a travel pedal.
14. A control apparatus of a construction machine according to
claim 13, further comprising: a travel detection device that
detects traveling or non-traveling, wherein: if the non-traveling
is detected with the travel detection device when the control
rotation speed is greater than the actual rotation speed, the input
torque control device decreases the input torque by an amount which
is greater than an amount set when the traveling is detected.
15. A wheeled hydraulic excavator, comprising: a variable
displacement hydraulic pump driven by a prime mover; a hydraulic
actuator driven with pressure oil discharged from the hydraulic
pump; a rotation speed detection device that detects an actual
rotation speed of the prime mover; and a control apparatus
according to claim 9.
16. An method for calculating an input torque which is implemented
by a hydraulic circuit including at least a variable displacement
hydraulic pump driven by a prime mover and a hydraulic actuator
driven with pressure oil discharged from the hydraulic pump,
comprising: calculating a standard torque in correspondence with a
deviation between a control rotation speed and an actual rotation
speed of the prime mover; setting a correction torque to zero if
the control rotation speed is greater than the actual rotation
speed and the deviation between them is smaller than or equal to a
predetermined value, but setting the correction torque to a
negative value if the deviation is larger than the predetermined
value; and calculating the input torque by adding the correction
torque to the standard torque.
17. A control apparatus of a construction machine according to
claim 10, wherein: the input torque control device sets an
adjustment amount of the input torque to zero if the control
rotation speed is greater than the actual rotation speed and the
deviation between them is below the predetermined value.
18. A control apparatus of a construction machine according to
claim 10, wherein: the input torque control device executes control
to increase the input torque in correspondence with increase in the
deviation if the control rotation speed is smaller than the actual
rotation speed, and if the control rotation speed is greater than
the actual rotation speed and the deviation between them is larger
than or equal to the predetermined value, a rate of change of the
input torque is set greater than a rate of change of the input
torque set when the control rotation speed is smaller than the
actual rotation speed.
19. A control apparatus of a construction machine according to
claim 10, wherein: the hydraulic actuator is a hydraulic motor for
traveling, and the operating member is a travel pedal.
20. A control apparatus of a construction machine according to
claim 19, further comprising: a travel detection device that
detects traveling or non-traveling, wherein: if the non-traveling
is detected with the travel detection device when the control
rotation speed is greater than the actual rotation speed, the input
torque control device decreases the input torque by an amount which
is greater than an amount set when the traveling is detected.
21. A wheeled hydraulic excavator, comprising: a variable
displacement hydraulic pump driven by a prime mover; a hydraulic
actuator driven with pressure oil discharged from the hydraulic
pump; a rotation speed detection device that detects an actual
rotation speed of the prime mover; and a control apparatus
according to claim 10.
Description
TECHNICAL FIELD
[0001] The present invention relates to a control apparatus of a
construction machine that controls an input torque that affects a
prime mover of the construction machine and to a method for
calculating the input torque.
BACKGROUND ART
[0002] Construction machines known in the related art include the
one disclosed in, for instance, Japanese Patent No. 2633095, which
has a traveling hydraulic motor driven with the discharged oil from
a variable displacement hydraulic pump which is driven by an
engine, and is capable of controlling an engine rotation speed in
response to an operation of a travel pedal as well as allowing the
vehicle to travel by controlling the quantity of the pressure oil
supplied to the hydraulic motor in response to the operation of the
travel pedal.
[0003] In the construction machine disclosed in the above-mentioned
publication, the input torque is controlled on the basis of the
following speed sensing control. That is, a target torque to
prevent an engine stall is calculated based on a deviation between
an actual engine rotation speed detected by a rotation speed sensor
and a target rotation speed corresponding to a position of a
governor lever of the engine, and then a target pump displacement
angle is calculated based on the target torque so as to control the
pump displacement angle. When calculating the target torque, the
operation is executed only to increase the input torque but not to
decrease the input torque. In this manner, the displacement angle
of the hydraulic pump is maintained greater than or equal to a
predetermined value, and as a result, smooth acceleration can be
secured.
[0004] In recent years, engines designed to handle exhaust gas have
been used in order to suppress the generation of black smoke. In
the engine designed to handle exhaust gas, the full load
performance curve is set such that the engine output torque in the
low speed range is smaller than a value for conventional engines.
More particularly, the maximum output torque of the engine is
shifted to the high speed range, and the torque is increased
gradually from the low speed range to the middle speed range
whereas the torque is increased sharply from the middle speed range
to the high speed range. As a result, the fuel consumption in the
low speed range can be reduced so as to suppress the generation of
black smoke.
[0005] The following problems would occur if the input torque was
controlled as described in the above-mentioned publication with
such an engine that copes with exhaust gas. That is, since the
input torque is not controlled to decrease in the construction
machine according to the above-mentioned publication, the input
torque may exceed the engine output torque when the vehicle is
starting traveling or climbing uphill and the travel load becomes
greater, which may cause an engine stall to occur.
DISCLOSURE OF THE INVENTION
[0006] An object of the present invention is to provide a control
apparatus of a construction machine suitable for being employed
with an engine designed to cope with exhaust gas, and a method for
calculating an input torque.
[0007] The present invention is adopted in a construction machine
having a variable displacement hydraulic pump driven by a prime
mover, a hydraulic actuator driven with pressure oil discharged
from the hydraulic pump, and a rotation speed detection means for
detecting an actual rotation speed of the prime mover. A control
apparatus of this construction machine includes a prime mover
control means for controlling a rotation speed of the prime mover
in accordance with an extent to which the operating means is
operated, and an input torque control means for adjusting an input
torque for the hydraulic pump based on a deviation between the
actual rotation speed detected by the rotation speed detection
means and a control rotation speed set through an operation of the
operating means, and executes control to decrease the input torque
if the control rotation speed is greater than the actual rotation
speed and the deviation between them is larger than or equal to a
predetermined value.
[0008] Furthermore, a control apparatus of the construction machine
includes a prime mover control means for controlling a rotation
speed of the prime mover in accordance with an extent to which the
operating means is operated, and an input torque control means for
adjusting an input torque for the hydraulic pump based on a
deviation between the actual rotation speed detected by the
rotation speed detection means and a control rotation speed set
through an operation of the operating means, and if the control
rotation speed is greater than the actual rotation speed and the
deviation between them is larger than or equal to a predetermined
value, control is executed to decrease the input torque by an
amount which is greater than an amount set when the deviation is
below the predetermined value.
[0009] In this manner, an engine stall can be prevented and
excellent acceleration can be achieved, and thus the control
apparatus is suitable for being used with an engine designed to
cope with exhaust gas.
[0010] It is preferable that an adjustment amount of the input
torque is set to zero if the control rotation speed is greater than
the actual rotation speed and the deviation between them is below
the predetermined value. If the control rotation speed is greater
than the actual rotation speed and the deviation between them is
larger than or equal to the predetermined value, a rate of change
of the input torque may be set greater than a rate of change of the
input torque set when the control rotation speed is smaller than
the actual rotation speed.
[0011] It is possible for the hydraulic actuator to be a hydraulic
motor for traveling and for the operating means to be a travel
pedal. The input torque during non-traveling may be decreased by an
amount which is greater than an amount set during traveling.
[0012] The present invention is ideal in an application in a
wheeled hydraulic excavator.
[0013] An input torque may be calculated by calculating a standard
torque in correspondence with a deviation between a control
rotation speed and an actual rotation speed of the prime mover,
setting a correction torque to zero if the control rotation speed
is greater than the actual rotation speed and the deviation between
them is smaller than or equal to a predetermined value, but setting
the correction torque to a negative value if the deviation is
larger than or equal to the predetermined value, and adding the
correction torque to the standard torque.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is an external view of an embodiment of a wheeled
hydraulic excavator in which the present invention is adopted;
[0015] FIG. 2 is a circuit diagram of a hydraulic circuit of a
control apparatus achieved in an embodiment of the present
invention;
[0016] FIG. 3 is a diagram of P-qp curve of a variable displacement
hydraulic pump;
[0017] FIG. 4 shows a full load performance curve of an engine used
in the embodiment of the present invention;
[0018] FIG. 5 is a block diagram of the control apparatus according
to the embodiment of the present invention;
[0019] FIG. 6 shows in detail a control circuit for an input
torque;
[0020] FIG. 7 shows in detail a control circuit for an engine
rotation speed;
[0021] FIG. 8 presents a flowchart of the control procedure of the
engine rotation speed; and
[0022] FIG. 9 shows diagrams illustrating operational
characteristics achieved by the control apparatus according to the
embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0023] An embodiment achieved by adopting a control apparatus of a
construction machine according to the present invention in a
wheeled hydraulic excavator is explained in reference to FIGS. 1
through 9.
[0024] As shown in FIG. 1, the wheeled hydraulic excavator includes
an undercarriage 1 and a revolving superstructure 2 rotatably
mounted atop the undercarriage 1. An operator's cab 3 and a work
front attachment 4 constituted with a boom 4a, an arm 4b and a
bucket 4c are provided at the revolving superstructure 2. The boom
4a is raised/lowered as a boom cylinder 4d is driven, the arm 4b is
raised/lowered as an arm cylinder 4e is driven and the bucket 4c is
engaged in a dig/dump operation as a bucket cylinder 4f is driven.
A traveling hydraulic motor 5, which is hydraulically driven, is
provided at the undercarriage 1, and the rotation of the traveling
motor 5 is transmitted to wheels 6 (tires) via a drive shaft and an
axle.
[0025] FIG. 2 shows a hydraulic circuit for traveling and for work.
A variable displacement hydraulic pump 10 is connected with the
hydraulic motor 5 via a control valve 11, and with a hydraulic
cylinder, for instance, the boom cylinder 4d via a control valve
12. Pilot ports of the control valve 11 are connected with a pilot
valve 14 via a forward/backward switching valve 13 whereas pilot
ports of the control valve 12 are connected with a pilot valve
15.
[0026] The forward/backward switching valve 13 is switched through
an operation of a switch not shown in the figure, and the pilot
valve 14 is operated in accordance with an extent to which a travel
pedal 14a is depressed. As the forward/backward switching valve 13
is set to a forward position or a backward position through a
switch operation and then the travel pedal 14a is operated, a pilot
pressure originating from a hydraulic source 16 is applied to the
control valve 11. In response, the pressure oil is supplied from
the hydraulic pump 10 to the hydraulic motor 5 as the control valve
11 is operated and then the hydraulic motor 5 rotates to allow the
vehicle to travel forward or backward.
[0027] On the other hand, the pilot valve 15 is operated according
to an extent to which an operating lever 15a is operated. A pilot
pressure from a hydraulic source 17 is applied to the control valve
12 as the operating lever 15a is operated. As the control valve 12
is operated, the pressure oil from the hydraulic pump 10 is
supplied to the boom cylinder 4d so as to enable the work
operation, for instance, the excavation with the boom cylinder 4d
being driven.
[0028] The hydraulic pump 10 is driven with an engine 20, and a
pump displacement angle qp is changed with a regulator 30. The
discharged oil pressure from the pump is fed back to the regulator
30 so as to execute the horsepower control. The horsepower control
is a so-called P-qp (pressure to pump displacement angle) control
shown in FIG. 3. In addition, the pump displacement amount pq is
also controlled in accordance with an input torque which is
calculated through the speed sensing control to be detailed later
in the present embodiment. Accordingly, the input torque is
increased or decreased as indicated by arrows shown in FIG. 3.
[0029] In this embodiment, the engine designed to cope with exhaust
gas is used so as to suppress the generation of black smoke. FIG. 4
shows characteristic diagrams of engine full load performance
curves with characteristics of the engine coping with the exhaust
gas being indicated with a solid line and characteristics of other
type of engine being indicated with a dotted line. The engine
coping with the exhaust gas is designed such that an output torque
T in the low speed range is small as shown in FIG. 4. More
particularly, a maximum output torque is shifted to the high speed
range, and the torque is set to increase gradually from the low
speed range to the middle speed range but to increase sharply from
the middle speed range to the high speed range. The fuel
consumption in the low speed range can be lowered by using the
engine with such characteristics, and the generation of black smoke
can be reduced.
[0030] FIG. 5 is a block diagram of the control apparatus according
to the present embodiment. A governor lever 21 of the engine 20 is
connected to a pulse motor 23 via a link mechanism 22 and the
engine rotation speed is adjusted with the rotation of the pulse
motor 23. Namely, the engine rotation speed increases as the pulse
motor 23 rotates forward, and the engine rotation speed decreases
with a reverse rotation of the pulse motor 23. The rotation of the
pulse motor 23 is controlled by a control signal from a controller
40 as described later. A potentiometer 24 is connected to the
governor lever 21 via the link mechanism 22, and the governor lever
angle corresponding to the rotation speed of the engine 20, which
is detected with the potentiometer 24, is input to the controller
40 as an engine control rotation speed N.theta..
[0031] A rotation speed sensor 31 that detects an actual rotation
speed Nr of the engine 20, a brake switch 32, a position sensor 33
that detects the position to which the forward/backward switching
valve 13 is switched, a detector 35 that detects an extent X to
which an operation member, i.e., a fuel lever 34 for instructing
the engine rotation speed is operated, and a pressure sensor 36
that detects a pilot pressure Pt representing the extent to which
the travel pedal 14a is depressed are also connected to the
controller 40.
[0032] As the brake switch 32 is switched to a traveling position,
a work position or a parking position, a work or traveling signal
is output from the brake switch 32. When the brake switch 32 is
switched to the traveling position, a parking brake is canceled and
the operation of a service brake is enabled through a brake pedal.
As the brake switch 32 is switched to the work position, the
parking brake and the service brake are both engaged. When it is
switched to the parking position, the parking brake is engaged. As
the brake switch 32 is switched to the traveling position, it
outputs an on signal, whereas it outputs an off signal when it is
switched to the work or parking position.
[0033] The controller 40 includes a torque control unit 40A for
controlling the input torque and a rotation speed control unit 40B
for controlling the engine rotation speed. FIG. 6 is a conceptual
diagram illustrating in detail the torque control unit 40A.
[0034] The torque control unit 40A includes a deviation calculation
unit 41 that calculates a deviation .DELTA.N between the actual
engine rotation speed Nr and the control rotation speed N.theta.,
standard torque calculation units 42 and 43 that calculate standard
torques TB1 and TB2 respectively, correction torque calculation
units 44 and 45 that calculate correction torques .DELTA.T1 and
.DELTA.T2 respectively, coefficient calculation units 46 and 47
that each calculate a coefficient, multiplication units 48 and 49
that multiply the correction torques .DELTA.T1 and .DELTA.T2 by the
coefficients respectively, adding units 50 and 51 that calculate
target input torques T1 and T2 by adding the multiplied correction
torques .DELTA.T1 and .DELTA.T2 to the standard torques T1 and T2
respectively, a selection unit 52 that selects one of the target
input torques T1 and T2, and a converting unit 53 that outputs a
control signal i for adjusting the input torque to the selected
target input torque T1 or T2.
[0035] Characteristics suited for work are each set in advance at
the standard torque calculation unit 42, the correction torque
calculation unit 44 and the coefficient calculation unit 46, and
characteristics suited for traveling are each set in advance at the
standard torque calculation unit 43, the correction torque
calculation unit 45 and the coefficient calculation unit 47.
[0036] Arithmetic operations executed at the torque control unit
40A are now explained in detail.
[0037] The deviation calculation unit 41 calculates the deviation
.DELTA.N (=Nr-N.theta.) between the engine actual rotation speed Nr
detected by the rotation speed sensor 31 and the control rotation
speed N.theta. detected by the potentiometer 24, and the deviation
.DELTA.N thus calculated is inputted to the correction torque
calculation units 44 and 45. The relationships between the
deviation .DELTA.N and each of the correction torques .DELTA.T1 and
.DELTA.T2 are stored in memory in advance at the correction torque
calculation units 44 and 45 respectively as shown in the figure,
and the correction torques .DELTA.T1 and .DELTA.T2 matching the
deviation .DELTA.N are individually calculated based upon the
characteristics of these relationships.
[0038] The characteristics set in the correction torque calculation
unit 44 indicate that the correction torque A T1 has a positive
value when the deviation .DELTA.N is positive and the correction
torque .DELTA.T1 increases proportionally as the deviation .DELTA.N
increases. The correction torque .DELTA.T1 is set to be a negative
value when the deviation .DELTA.N is negative and the correction
torque .DELTA.T1 decreases (or |.DELTA.T1| increases)
proportionally as the deviation .DELTA.N decreases. The inclination
of the characteristics with the deviation .DELTA.N being a positive
value is equivalent to the inclination of the characteristics when
the deviation .DELTA.N is a negative value.
[0039] The characteristics set in the correction torque calculation
unit 45 indicate, on the other hand, that the correction torque
.DELTA.T2 has a positive value when the deviation .DELTA.N is
positive and the correction torque .DELTA.T2 increases
proportionally as the deviation .DELTA.N increases. Contrary to
this, when the deviation .DELTA.N is a negative value and in the
range between 0 and a predetermined value N2, the correction torque
.DELTA.T2 is 0, and if the deviation .DELTA.N is smaller than the
predetermined value N2, the correction torque .DELTA.T2 decreases
proportionally as the deviation .DELTA.N decreases. The inclination
of the characteristics with the deviation .DELTA.N being smaller
than the predetermined value N2 is steeper than the inclination of
the characteristics when the deviation .DELTA. N is positive.
[0040] The relationships between the control rotation speed
N.theta. and each of the standard torques TB1 and TB2 are stored in
memory in advance at the standard torque calculation units 42 and
43 respectively as shown in the figure, and the standard torques
TB1 and TB2 matching the control rotation speed N.theta. are
individually calculated based upon the characteristics of these
relationships. The characteristics in which the coefficients
increase in proportion to the control rotation speed N.theta. are
stored in memory in advance at the coefficient calculation units 46
and 47 as shown in the figure, and the coefficients matching the
control rotation speed N.theta. are calculated based upon these
characteristics. The multiplication units 48 and 49 multiply the
correction torques .DELTA.T1 and .DELTA.T2 calculated at the
correction torque calculation units 44 and 45 by the coefficients
calculated at the coefficient calculation units 46 and 47
respectively.
[0041] The adding units 50 and 51 calculates the target input
torques T1 and T2 by adding the correction torques .DELTA.T
multiplied at the multiplication units 48 and 49 to the standard
torques TB1 and TB2 calculated at the standard torque calculation
units 42 and 43 respectively.
[0042] The selection unit 52 makes a decision as to whether or not
the vehicle is traveling based on the signals provided from the
brake switch 32, the position sensor 33 and the pressure sensor 36.
If the brake switch 32 has been turned off, the forward/backward
switching valve 13 is set to a position other than the neutral
position and the pilot pressure Pt is greater than a predetermined
value, it is decided that the vehicle is traveling, otherwise, it
is decided the vehicle is not traveling. The target input torque T2
is selected if the vehicle is traveling, and the target input
torque T1 is selected when the vehicle is not traveling, for
instance, when it is engaged in work operations.
[0043] The converting unit 53 calculates a control signal i
corresponding to the selected target input torque T1 or T2. A
cylinder for regulating the displacement angle and a solenoid valve
for controlling the flow of pressure oil to the cylinder are
mounted at the pump regulator 30 although not shown in the figures,
and the control signal i outputted from the converting unit 53 is
sent to this solenoid valve. In response, the pump displacement
angle qp changes so as to regulate the input torque to the target
input torque T1 or T2.
[0044] FIG. 7 is a conceptual diagram illustrating in detail the
rotation speed control unit 40B. As shown in the figure, the
relationship between the detection value X provided by the detector
35 and a target rotation speed Nx is stored in memory in advance at
a target rotation speed calculation unit 61, and the target
rotation speed Nx corresponding to the extent to which the fuel
lever 34 is operated is calculated based upon the characteristics
of the relationship. The relationship between the detection value
Pt provided by the pressure sensor and a target rotation speed Nt
is stored in memory in advance at a target rotation speed
calculation unit 62 as shown in the figure, and the target rotation
speed Nt matching the extent to which the travel pedal 14a is
operated is calculated based upon the characteristics of the
relationship.
[0045] These characteristics stored in the target rotation speed
calculation units 61 and 62 each indicate linear increases in the
target rotation speeds Nx and Nt from the idling rotation speed Ni
as the extent of operation increases. A maximum target rotation
speed Nxmax set at the target rotation speed calculation unit 61 is
set smaller than a maximum speed of the engine 20, and a maximum
target rotation speed Ntmax set at the target rotation speed
calculation unit 62 is set substantially equal to the maximum speed
of the engine 20. Therefore, the maximum target rotation speed
Ntmax is larger than the maximum target rotation speed Nxmax.
[0046] The selection unit 63 selects the larger value between the
target rotation speeds Nx and Nt calculated at the target rotation
speed calculation units 61 and 62. A servo control unit 57 compares
the selected rotation speed (rotation speed command value Nin) with
the control rotation speed N.theta. corresponding to the
displacement quantity of the governor lever 21 detected with the
potentiometer 24. Then, it controls the pulse motor 23 through the
procedure shown in FIG. 8 so as to match the two values.
[0047] First, the rotation speed command value Nin and the control
rotation speed N.theta. are individually read in step S21 before
proceeding to step S22 in FIG. 8. Then, in step S22, the results of
subtracting Nin from N.theta. are stored as a rotation speed
difference A in memory, and in step S23, a decision is made as to
whether or not |A|.gtoreq.K is true with regard to the rotation
speed difference A and a predetermined reference rotation speed
difference K. If an affirmative decision is made, the operation
proceeds to step S24 to decide whether or not the rotation speed
difference A is greater than 0. If A>0, the control rotation
speed N.theta. is greater than the rotation speed command value
Nin, i.e., the control rotation speed is higher than the target
rotation speed and, accordingly, a signal constituting a command
for a motor reverse rotation is output to the pulse motor 43 in
step S25 in order to lower the engine rotation speed. In response,
the pulse motor 23 rotates in the reverse direction, thereby
lowering the engine rotation speed.
[0048] If, on the other hand, A.ltoreq.0, the control rotation
speed N.theta. is lower than the rotation speed command value Nin,
i.e., the control rotation speed is lower than the target rotation
speed and, accordingly, a signal constituting a command for a motor
forward rotation is output in step S26 in order to raise the engine
rotation speed. In response, the pulse motor 23 rotates forward,
thereby raising the engine rotation speed. If a negative decision
is made in step S23, the operation proceeds to step S27 to output a
motor stop signal and, as a result, the engine rotation speed is
sustained at a constant level. Once the processing in one of steps
S25 through S27 is executed, the operation returns to the start
point.
[0049] Next, the operation that characterizes the control device
achieved in this embodiment is explained.
[0050] The brake switch 32 is set to the traveling position and the
forward/backward switching valve 13 is switched to the forward or
backward position when the vehicle is to travel. As the fuel lever
34 is set to the idling position and the travel pedal 14a is
depressed to the maximum extent in this state, the traveling motor
5 is caused to revolve with the pressure oil discharged from the
hydraulic pump 10 so as to allow the vehicle to start traveling.
The selection unit 63 selects the target rotation speed Nt as the
rotation speed command value Nin since the target rotation speed Nt
set through the travel pedal 14a is greater than the target
rotation speed Nx set through the fuel lever 34 at this time, and
the governor lever position is controlled so as to match the actual
rotation speed with the rotation speed command value Nin through
the procedure shown in the FIG. 8. In response, the position of the
governor lever 21 changes a great deal and the control rotation
speed N.theta. increases as indicated with the broken line shown in
FIG. 9(a).
[0051] As the control rotation speed N.theta. increases, the actual
engine rotation speed Nr also increases, however, there is a time
lag until the actual engine rotation speed Nr reaches the control
rotation speed N.theta., causing the deviation .DELTA.N to be a
negative value during this period. In this case, the engine output
torque T, characteristics of which are based on the characteristics
shown in the FIG. 4, changes as shown in the FIG. 9(b).
[0052] The selection unit 52 selects the target input torque T2
during the vehicle traveling. Accordingly, the torque control unit
40A executes the speed sensing control based on the characteristics
set at the correction torque calculation unit 45. Since the
deviation |.DELTA.N| is larger than the predetermined value N2
immediately after the beginning of the operation of the travel
pedal 14a, the correction torque A T2 calculated at the correction
torque calculation unit 45 shows a negative value. In this manner,
the input torque T2 is set smaller than the output torque T when
the vehicle is starting to travel as shown in the FIG. 9(b) so as
to avoid the engine stall.
[0053] The negative correction torque .DELTA.T2 decreases as the
deviation |.DELTA.N| decreases in response to the increase in the
actual engine rotation speed Nr, and then the correction torque
.DELTA.T2 is set to 0 when the deviation |.DELTA.N| becomes equal
to the predetermined value N2 or smaller. By setting the correction
torque .DELTA.T to 0 before the deviation |.DELTA.N| reaches 0 as
described above, the input torque T2 can be brought back to the
value corresponding to the standard torque TB2 quickly so as to
achieve excellent acceleration. It is to be noted that even if the
input torque T2 exceeds the output torque T for a short period of
time during the increase of the input torque T2 as shown in FIG.
9(b), a difference (T-T2) between the output torque and the input
torque is small enough not to cause any problems from a practical
point of view. The above-mentioned embodiment can be adopted
effectively to vehicles with a great load, therefore, it can be
equally adopted, not only to a vehicle starting to travel, but also
to a vehicle climbing uphill.
[0054] The characteristic T20 shown in FIG. 9(b) show conventional
characteristics of the input torque by which the correction torque
.DELTA.T is uniformly maintained at 0 with the deviation .DELTA.N
being a negative value. According to this characteristics, the
input torque T20 does not become smaller than the standard torque
when the deviation .DELTA.N is negative. In this manner, the engine
input torque T20 exceeds the output torque T when the vehicle at
which an engine coping with exhaust gas with a small output torque
is mounted is starting to travel, and as a result the engine stall
may occur.
[0055] To engage the vehicle in work, the brake switch 32 is set to
the work position and the forward/backward switching valve 13 is
set to the neutral position. The selection unit 63 of the rotation
speed control unit 40B selects the target rotation speed Nx set
through the fuel lever 34 as the rotation speed command value Nin
if the fuel lever 34 is operated to a certain extent instead of
operating the travel pedal 14a in this condition, and the governor
lever position is controlled so as to match the actual rotation
speed with the control speed command value Nin. At this time, the
selection unit 52 of the torque control unit 40A selects the target
input torque T1, and the torque control unit 40A executes the speed
sensing control based on the characteristics set at the correction
torque calculation unit 44. The input torque T1 is always smaller
than the output torque T as shown in FIG. 9(c) because the
correction torque .DELTA.T corresponding to the negative deviation
.DELTA.N is calculated to be a negative value at the correction
torque calculation unit 44.
[0056] According to the embodiment, the following advantages can be
achieved. [0057] (1) The correction torque .DELTA.T2 is set to be a
negative value if the deviation .DELTA.N between the actual engine
rotation speed Nr and the control rotation speed N.theta. is
negative and |.DELTA.N| is greater than the predetermined value N2,
and the correction torque .DELTA.T2 is set to be 0 if the
|.DELTA.N| is equal to or less than the predetermined value N2. By
doing this, the input torque T2 can be set smaller than the output
torque T when the vehicle is starting to travel even if the engine
coping with exhaust gas is installed therein, and thus the engine
stall can be prevented from happening and excellent acceleration
can be obtained. [0058] (2) The inclination of the correction
torque .DELTA.T corresponding to the negative deviation .DELTA.N
with |.DELTA.N| being greater than the predetermined value N2 is
set to be greater than the inclination of the correction torque
.DELTA.T corresponding at least to the deviation .DELTA.N which is
a positive value. Accordingly, the input torque T2 can be brought
back to the standard torque TB2 quickly as the deviation .DELTA.N
approaches the predetermined value N2, and the hunting can be
prevented from occurring when the deviation .DELTA.N is a positive
value. [0059] (3) The characteristics based upon which the
correction torques .DELTA.T are calculated in a traveling state and
in a non-traveling state of the vehicle are set individually, and
since the acceleration performance does not count so much in the
non-traveling state, the correction torque .DELTA.T is set to be a
negative value when the deviation .DELTA.N is negative. As a
result, the input torque T1 can be maintained smaller than or equal
to the output torque T when the vehicle is engaged in work
operations.
[0060] While the correction torque .DELTA.T2 is set to 0 when the
deviation .DELTA.N is in the range of N2.ltoreq..DELTA.N.ltoreq.0
according to the above-described embodiment, the correction torque
.DELTA.T2 does not have to be set to 0 as long as the
characteristics of the correction torque .DELTA.T2 is defined such
that the inclination of the correction torque .DELTA.T2
corresponding to the negative deviation .DELTA.N has two different
levels with reference to the predetermined value N2.
[0061] While the explanation is given on an example to ensure the
acceleration performance of the traveling hydraulic motor 5 during
traveling, the present invention is not to be limited to this
example and may be applied, for instance, to a revolving hydraulic
motor that revolves the revolving superstructure. Accordingly, an
operation means is also not limited to the travel pedal 14a.
INDUSTRIAL APPLICABILITY
[0062] While an explanation is given above on an example in which a
wheeled hydraulic excavator represents an example of a construction
machine in which the present invention may be adopted, the present
invention may also be adopted in other types of construction
machines such as non-wheel construction machines.
* * * * *